The present disclosure relates to photonic integrated circuit (PIC) die packaging, and more specifically, to PIC die packaging using magnetics to position an optical element such as optical fibers.
Current photonic packages consisting of V-groove photonic integrated circuit (PIC) dies require complex packaging integration schemes. In particular, optical elements such as optical fibers or optical fiber arrays are optically coupled to the PIC die and internal waveguides thereof. Conventionally, V-groove fiber optic receptacles in a surface of the PIC die provide an alignment and retention feature for passive alignment of an optical fiber to couple light from an end surface (typically, 125 micrometers (um) fiber outer diameter with a 9 um fiber core) thereof to an exposed end of an optical waveguide (approximately 200×450 nanometers (nm)) in the PIC die. In this process, optical fibers are positioned by a pick-and-place tool into respective V-groove fiber optic receptacles in a surface of the PIC die. V-groove fiber optic receptacles enable two linear contact regions for each optical fiber to align the optical fiber core to a silicon waveguide in the PIC die. The two linear contact regions ensure passive optical alignment when the optical fiber(s) is fully seated on the V-groove sidewalls, with an optical fiber end to waveguide end separation of perhaps +/−5 um. Once in position, the optical fibers are secured in place using a refractive index (RI) matching optical adhesive, which is ultraviolet (UV) cured to tack the adhesive, often prior to full curing using a thermal cure process.
One challenge in achieving high alignment accuracy is applying a uniform force along the optical fiber surface near the coupling site to ensure the optical fiber to V-groove contact and prevent optical fibers from lifting up at the coupling interface, i.e., to maintain position and pitch alignment. To address this situation, glass lids have been used to force the optical fibers into the V-groove fiber optic receptacles. In this arrangement, the glass lids are placed over the optical fiber(s) and pressed down to force the optical fiber(s) into place. More specifically, the pick-and-place tool tip is used to position and then apply a downward force to the glass lids. This situation is not ideal because the pick-and-place tool tips are typically not designed to apply force during adhesive cure, and the process is not readily repeatable.
Another challenge is achieving optimal UV radiation cure of the adhesive to tack the fibers in place. In particular, the glass lids are transparent to allow UV radiation to pass therethrough to adequately cure the UV curable adhesive. However, during the time that the pick-and-place tool tip is applying a force on the lid, it blocks UV radiation from curing the adhesive and/or causes shadowing effects, inhibiting cure. The result is that the UV curable adhesive does not cure in certain locations, or the PIC die must remain for a longer time than desired in the optical fiber assembly tool. UV transparent pick-and-place tool tips have been proposed, but they present concerns with adhesive contamination of the tip. UV transparent polymer or glass fiber blocks on which arrays of optical fibers are pre-attached have been employed, but they also must be picked and placed into position and mechanically forced down to position the optical fibers. Consequently, they present many of the same challenges already described.